Major Advances in Phased Arrays: Part 1

The maturation of electronically steerable phase-phase scanned arrays over the last 35 years

Major Advances in Phased Arrays: Fast One

This article is the first of a two-part series that describes the major accomplishments in phased arrays, and new-age MMIC ground-based and airborne arrays. Significant advances have been made in the last 35 years in the area of electronically steerable phase-phase scanned arrays, that is, arrays that scan in two dimensions, and many more advances will occur in the future. This article discusses highlights of some of the major advances in this technology in the US, the spread of the activity for the development of phase-phase scanned arrays around the world over the last decade and the dramatic entrance into the new era of active MMIC phase-phase steered arrays for ground and airplane platforms in large quantities.

Over the last few decades, phase-phase scanned arrays have come a long way. Some of the phased arrays developed and deployed over the last 35 years have had production runs of over 50. Among the systems using phased arrays are the Patriot,1 airborne early-warning ground integration system (AEGIS)1 and Russian Flap Lid radars, shown in Figures 1, 2 and 3 , respectively, as well the TPQ-37,1 B-11 and GPN-221,2 radar systems.

Approximately one million elements and phase shifters have been manufactured for the Patriot, AEGIS and Flap Lid radars. For some of these phased arrays, only one system has been produced. However, even one radar can result in relatively high volume module production. For example, for the COBRA DANE radar system's phased array, shown in Figure 4 , 15,360 phase shifters and 34,769 elements were manufactured as part of the array.

The AN/TPS-25 was the first radar phased array put into production. Initially, 11 of these phased arrays were built for the US Air Force, followed by seven for the Australian government. It is interesting that the first phased-array antenna put into production is actually one-half reflector antenna and one-half phased array. The antenna consists of a large reflector fed by a small array feed comprising 824 ferrite phase shifters, as shown in Figure 5 .

The large reflector provides the required high gain, while the small array provides the electronic scanning needed over a limited scan angle: 20¡ in azimuth and 15¡ in elevation. This X-band radar is used for guiding aircraft on the runway during final approach for conditions of bad as well as good weather. A derivative of this radar, the GPN-22 precision approach radar (PAR), shown in Figure 6 , is still in production.

Sixty of these systems have been deployed around the world for commercial and military use. The PAVE PAWS system, shown in Figure 7 , is the first solid-state phase-phase scanned array deployed.

This radar has two faces, each with 1792 R) 330 W UHF modules feeding 1792 bent cross dipole radiating elements. There are an additional 885 dipole elements that do not radiate (dummy elements) for a total transmit/receive (T/of 2677 elements. These elements are spread over a circular diameter of 72.5 feet. Actually, there are approximately 2600 additional unused elements out to a diameter of 102 feet for a total of approximately 5300 elements. The elements in this outer ring beyond the 72.5 feet are reserved for a future 10 dB increase in system sensitivity. Table 1 lists examples of the more prominent phased-array systems. A Decade of Phase-phase Scanned Arrays Recent years have seen the development and deployment of phased arrays by several countries around the world. For example, the Swedish ARTHUR C-band artillery-locating system uses a traveling-wave tube (TWT) transmitter, as shown in Figure 8 .

The Swedish Erieye airborne early-warning radar system uses an S-band solid-state phased array placed in a dorsal fin over the top of the aircraft. The system has approximately 200 modules, which are shared with the array faces on both sides of the dorsal fin. The Erieye system is shown in Figure 9 .

The antennas are placed on the left and right sides of the aircraft forward of the wing, and on the underside toward the nose and tail of the aircraft. The system has been sold to Chile. Israel has also developed a theater missile defense system that is capable of detection ranges of hundreds of kilometers. This radar uses an L-band solid-state active phased array. Two such systems have been built.4 India has its own phased-array SAM-D system. The European multifunction phased-array C-band shipboard radar is being built by Alenia (Italy) with the participation of Marconi Co. (UK). This long-range (180 km) system uses a TWT transmitter, and the phase-phase scanned array rotates at 60 rpm.5 The Thomson-CSF medium-range (70 km) phase-phase scanned X-band Arabel shipboard radar uses a space-fed array that also rotates at 60 rpm.6 The New Age of MMIC T/R Modules Ground-based MMIC Phased-array Systems An exciting new age of active phased-array antennas has begun using MMIC T/R modules, a technology that enables the production of solid-state T/R modules at a lower cost. Table 2 lists two such systems. The first system is the theater high altitude area defense (THAAD; formerly called GBR) X-band ground-based radar, which has 25,344 MMIC T/R modules and radiating elements,7 as shown in Figure 11 .

Three of these systems have been built. The first array was 50 percent populated with radiating elements and modules while the second and third arrays were populated fully. Approximately 60,000 MMIC T/R modules have been built for these systems. This program demonstrated that MMIC T/R modules could be manufactured for less than $1000 each at the end of the production run. The enabling technology base for achieving this module manufacturing efficiency in GaAs was derived from the Advanced Research Projects Agency/Tri-service Microwave and Millimeter Wave Monolithic Integrated Circuits program.8 Many more of the THAAD systems are scheduled to be built. The second MMIC active phased-array system is the counter battery radar (COBRA) artillery and mortar weapon-locating system, which is shown in Figure 12 .

This system has 2700 MMIC T/R C-band modules and radiating elements in its antenna. Three of these systems have been built. MMIC Arrays for Fighter Aircraft A number of countries are in the process of developing active phased arrays using MMIC T/R modules for fighter aircraft, including the US for the F-22 fighter; Japan for the FSX; the consortium of France, Germany and the UK developing the airborne multiroll solid-state active-array radar (AMSAR);9 and Sweden, which is developing the active electronically scanned antenna (AESA).10 All of these radar systems operate at X-band. The 424 F-22 X-band phased arrays, shown in Figure 13 , are scheduled to be built, each having approximately 2000 elements and MMIC T/R modules for a total production run of approximately one million MMIC T/R modules.

Conclusion

Electronically steerable phase-phase scanned arrays have matured greatly over the last 35 years. There are now radar systems all over the world that have incorporated this technique for antenna steering, the latest of which incorporate low cost MMIC components. These advances now allow the phased array to be used in high volume ground and airborne applications. Part two of this series will cover the emergence of MMIC arrays in large quantities into space-age telecommunications - IRIDIUM,¨ Globalstar and, potentially, Teledesic. Also covered will be research and development work in the area of electronically steerable laser and optical beams using row/column steering, the microwave row/column ferroelectric scanned array, the electronically steerable plasma mirror antenna, an aggressive wafer integration MMIC 94 GHz missile seeker phase-phase scanned array, the row/column scanned RADANT array antenna, the C- to Ku-band multi- user shared-aperture MMIC phase-phase steered array and digital beamforming including space-time adaptive processing.

11. J. Rhea, "Active Array Antennas Head for the Skies," Military and Aerospace Electronics, August 1996.

Eli Brookner received his BSEE degree from the City College of New York in 1953, and his MS and DSc degrees in electrical engineering from Columbia University in 1955 and 1962, respectively. Since 1962, he has been at Raytheon Co., where he is presently a consulting scientist in Sudbury, MA. Brookner conceived and helped design the Wake Measurement Radar, the first TWT radar put into space. He has been technical director for a number of space-based radar programs. Recently, he completed work on future improvements to the worldwide satellite-cellular IRIDIUM communications system and future commercial high data rate communications systems. Brookner is a member of Eta Kappa Nu and Tau Beta Pi, a fellow of the American Institute of Aeronautics and Astronautics, an IEEE fellow and a member of the International Union of Radar Science (URSI; commissions B and C).